Described below is a control method for a rolling mill train, wherein an adjusting device acting on a first roll stand of the rolling mill train is controlled during rolling of strip sections taking at least one control parameter into account.
The method may be implemented using a computer program containing machine code which can be processed directly by a control computer for a rolling mill train and the processing of which by the control computer causes the control computer to carry out such a control method.
A control computer for a rolling mill train is programmed such that it carries out such a control method during ongoing operation.
Also described below is a rolling mill train for strip rolling, the rolling mill train including at least a first roll stand and being equipped with such a control computer.
Temperature fluctuations over the width and length of the strip can result in considerable malfunctions during rolling. The changing material hardness causes variations in the rolling force which can in turn lead to other roll stand reactions which, for their part, result in a change in the roll gap profile. Examples of such roll stand reactions are roll flattening, roll deflection and stand spring. Added to these are a change in the roll crowning due to contact of the work rolls with the differentially heated strip. This also affects the roll gap geometry. If such changes in the roll gap profile are not taken into account, this will result in gauge, profile and flatness defects.
The known setpoint value calculation for rolling mill trains (pass schedule calculation) can only make limited provision for temperature variations in the longitudinal direction (head, strip and tail temperature) and none at all in the strip width direction. Until now, such effects have sometimes been compensated using automatic gauge control (AGC) which at least partly corrects the setting deviations due to roll stand reaction. In addition, techniques are known in which a rolling force measurement in the first roll stand of a multi-stand rolling mill train is used for feed-forward control of the remaining stands.
Both procedures have their disadvantages. For example, automatic gauge control (AGC) cannot react to variations in the temperature profile across the width of the strip. Above all, any asymmetry in material strength (e.g. caused by a temperature wedge) and, associated therewith, any roll stand reaction asymmetry is not taken into account. Furthermore, variation of the roll crown cannot be detected or can only be detected with a delay. Feed-forward control of the stands of a multi-stand rolling mill train by rolling force measurement in the first roll stand of the rolling mill train cannot, by its very principle, be used for a single-stand train.
Both known techniques have a further disadvantage in that they cannot utilize selective roll cooling in order to adapt the roll crown. Selective adaptation of the roll crown is useful in particular if the other actuating elements for influencing the roll gap shape (e.g. roll reverse bending and roll displacement) are at their limits of adjustment, e.g. in the case of increased rolling force due to a localized temperature drop.
This problem is particularly prevalent in continuous casting and rolling plants where there is no more than limited compensation for temperature variations in the strip, so that temperature profiles (over the length and/or the strip width) have not evened out before the strip reaches the mill stand or stands. Temperature variations can also occur in hot-rolled wide strip trains, e.g. due to the so-called skidmarks or uneven through-heating of the cast slab in the furnace.
DE 101 56 008 A1 and, with identical content, US 2004/205 951 A1 disclose a control method for a rolling mill train,                wherein a strip section temperature is determined in each case for strip sections upstream of the first roll stand,        wherein the strip section temperatures for the time of rolling of the respective strip section in the first roll stand are included in the calculation in real time by a strip model.        
In DE 101 56 008 A1, the temperature behavior and possibly also the phase transformation of the strip sections are determined purely with the aim of suitably adjusting strip heating and/or strip cooling. DE 101 56 008 A1 makes no provision for using the determined temperature in connection with the rolling process as such.
WO 2008/043 684 A1 discloses a control method for a rolling mill train,                wherein a strip section temperature is determined in each case for strip sections upstream of a first roll stand of the rolling train,        wherein the strip section temperatures for the time of rolling of the respective strip section in the first roll stand are predicted using a strip model on the basis of the temperatures determined,        wherein, using the predicted temperatures of the strip sections, at least one respective control parameter for rolling of the strip sections in the first roll stand is determined,        wherein an adjusting device acting on the first roll stand is controlled during rolling of the respective strip section taking the respective control parameter determined into account.        
EP 2 301 685 A1 discloses a control method for a rolling mill train, wherein in respect of sections of a strip, a respective temperature of the strip sections is determined ahead of a first roll stand of the rolling train. Based on a strip model and with reference to the temperatures that have been determined, the temperatures of the strip sections are predicted using a prediction horizon that corresponds to a plurality of strip sections.